ref: 37a8fc6168b3bf82df198fb20be5a8a53996187c
dir: /sys/src/libc/power/vlop.s/
#define BDNZ BC 16,0, /* * 64/64 division adapted from powerpc compiler writer's handbook * * (R3:R4) = (R3:R4) / (R5:R6) (64b) = (64b / 64b) * quo dvd dvs * * Remainder is left in R7:R8 * * Code comment notation: * msw = most-significant (high-order) word, i.e. bits 0..31 * lsw = least-significant (low-order) word, i.e. bits 32..63 * LZ = Leading Zeroes * SD = Significant Digits * * R3:R4 = dvd (input dividend); quo (output quotient) * R5:R6 = dvs (input divisor) * * R7:R8 = tmp; rem (output remainder) */ TEXT _divu64(SB), $0 MOVW a+0(FP), R3 MOVW a+4(FP), R4 MOVW b+8(FP), R5 MOVW b+12(FP), R6 /* count the number of leading 0s in the dividend */ CMP R3, $0 /* dvd.msw == 0? R3, */ CNTLZW R3, R11 /* R11 = dvd.msw.LZ */ CNTLZW R4, R9 /* R9 = dvd.lsw.LZ */ BNE lab1 /* if(dvd.msw != 0) dvd.LZ = dvd.msw.LZ */ ADD $32, R9, R11 /* dvd.LZ = dvd.lsw.LZ + 32 */ lab1: /* count the number of leading 0s in the divisor */ CMP R5, $0 /* dvd.msw == 0? */ CNTLZW R5, R9 /* R9 = dvs.msw.LZ */ CNTLZW R6, R10 /* R10 = dvs.lsw.LZ */ BNE lab2 /* if(dvs.msw != 0) dvs.LZ = dvs.msw.LZ */ ADD $32, R10, R9 /* dvs.LZ = dvs.lsw.LZ + 32 */ lab2: /* determine shift amounts to minimize the number of iterations */ CMP R11, R9 /* compare dvd.LZ to dvs.LZ */ SUBC R11, $64, R10 /* R10 = dvd.SD */ BGT lab9 /* if(dvs > dvd) quotient = 0 */ ADD $1, R9 /* ++dvs.LZ (or --dvs.SD) */ SUBC R9, $64, R9 /* R9 = dvs.SD */ ADD R9, R11 /* (dvd.LZ + dvs.SD) = left shift of dvd for */ /* initial dvd */ SUB R9, R10, R9 /* (dvd.SD - dvs.SD) = right shift of dvd for */ /* initial tmp */ MOVW R9, CTR /* number of iterations = dvd.SD - dvs.SD */ /* R7:R8 = R3:R4 >> R9 */ CMP R9, $32 ADD $-32, R9, R7 BLT lab3 /* if(R9 < 32) jump to lab3 */ SRW R7, R3, R8 /* tmp.lsw = dvd.msw >> (R9 - 32) */ MOVW $0, R7 /* tmp.msw = 0 */ BR lab4 lab3: SRW R9, R4, R8 /* R8 = dvd.lsw >> R9 */ SUBC R9, $32, R7 SLW R7, R3, R7 /* R7 = dvd.msw << 32 - R9 */ OR R7, R8 /* tmp.lsw = R8 | R7 */ SRW R9, R3, R7 /* tmp.msw = dvd.msw >> R9 */ lab4: /* R3:R4 = R3:R4 << R11 */ CMP R11,$32 ADDC $-32, R11, R9 BLT lab5 /* (R11 < 32)? */ SLW R9, R4, R3 /* dvd.msw = dvs.lsw << R9 */ MOVW $0, R4 /* dvd.lsw = 0 */ BR lab6 lab5: SLW R11, R3 /* R3 = dvd.msw << R11 */ SUBC R11, $32, R9 SRW R9, R4, R9 /* R9 = dvd.lsw >> 32 - R11 */ OR R9, R3 /* dvd.msw = R3 | R9 */ SLW R11, R4 /* dvd.lsw = dvd.lsw << R11 */ lab6: /* restoring division shift and subtract loop */ MOVW $-1, R10 ADDC $0, R7 /* clear carry bit before loop starts */ lab7: /* tmp:dvd is considered one large register */ /* each portion is shifted left 1 bit by adding it to itself */ /* adde sums the carry from the previous and creates a new carry */ ADDE R4,R4 /* shift dvd.lsw left 1 bit */ ADDE R3,R3 /* shift dvd.msw to left 1 bit */ ADDE R8,R8 /* shift tmp.lsw to left 1 bit */ ADDE R7,R7 /* shift tmp.msw to left 1 bit */ SUBC R6, R8, R11 /* tmp.lsw - dvs.lsw */ SUBECC R5, R7, R9 /* tmp.msw - dvs.msw */ BLT lab8 /* if(result < 0) clear carry bit */ MOVW R11, R8 /* move lsw */ MOVW R9, R7 /* move msw */ ADDC $1, R10, R11 /* set carry bit */ lab8: BDNZ lab7 ADDE R4,R4 /* quo.lsw (lsb = CA) */ ADDE R3,R3 /* quo.msw (lsb from lsw) */ lab10: MOVW qp+16(FP), R9 MOVW rp+20(FP), R10 CMP R9, $0 BEQ lab11 MOVW R3, 0(R9) MOVW R4, 4(R9) lab11: CMP R10, $0 BEQ lab12 MOVW R7, 0(R10) MOVW R8, 4(R10) lab12: RETURN lab9: /* Quotient is 0 (dvs > dvd) */ MOVW R4, R8 /* rmd.lsw = dvd.lsw */ MOVW R3, R7 /* rmd.msw = dvd.msw */ MOVW $0, R4 /* dvd.lsw = 0 */ MOVW $0, R3 /* dvd.msw = 0 */ BR lab10